The present invention relates to a heat-sensitive lithographic printing plate precursor suitable for a computer-to-plate system requiring no development-processing. More specifically, the present invention is concerned with a heat-sensitive lithographic printing plate precursor on which images can be recorded by infrared ray scanning exposure based on digital signals, and besides, which can be mounted in a printing machine (i.e., a printing press) after recording images are recorded thereon and subjected to printing operations without going through a conventional liquid development process.
A great many pieces of research have been done on the lithographic printing plate precursors suitable for computer-to-plate systems in which significant headway has recently been made. Of those plate precursors, lithographic printing plate precursors of the type which can be mounted in a printing machine without performing development after exposure and can undergo printing operations have been studied more actively with the aims of further streamlining the plate-making process and solving liquid waste disposal problems, and various methods have been proposed. One of the promising methods hitherto proposed consists in using a heat-sensitive lithographic printing plate precursor having as an image-forming layer a hydrophilic layer comprising a hydrophilic binder polymer and fine particles of hydrophobic thermoplastic polymer dispersed therein. More specifically, the method utilizes a phenomenon that, when heat is applied to the hydrophilic layer, the fine particles of hydrophobic thermoplastic polymer are fused to convert the water-receptive surface into an ink-receptive image area.
As a way of eliminating a processing step from the method of utilizing thermal fusion of fine particles of hydrophobic thermoplastic polymer, there is known the system referred to as on-press development wherein an exposed printing plate precursor is mounted on the cylinder of a printing machine and thereto a fountain solution and ink are fed while rotating the cylinder to result in removal of non-image areas from the printing plate precursor. In other words, this system is characterized in that the printing plate precursor after exposure is mounted in a printing machine as it is and the processing thereof is completed during the usual printing process.
In order that lithographic printing plate precursors acquire suitability for such on-press development, it is required for them to have not only a hydrophilic layer soluble in a fountain solution and an ink solvent but also illuminated handling capabilities so as to fit the development on a printing machine installed in a bright room.
For instance, Japanese Patent 2938397 discloses the lithographic printing plate precursor having on a water-receptive substrate a photosensitive layer (hydrophilic layer) containing fine particles of thermoplastic hydrophobic polymer in a condition that they are dispersed in a hydrophilic binder polymer. The publication cited above describes that on-press development with a fountain solution and/or ink can be achieved when the lithographic printing plate precursor is mounted on the cylinder of a printing machine after the fine particles of thermoplastic hydrophobic polymer coalesce thermally by being exposed to infrared ray laser beams to form images in the printing plate precursor.
In addition, JP-A-9-127683 (the term xe2x80x9cJP-Axe2x80x9d as used herein means an xe2x80x9cunexamined published Japanese patent applicationxe2x80x9d) and WO99-10186 also describe that printing plates can be made by on-press development after thermal coalescence of thermoplastic fine particles.
Although such a method as to form images by thermal coalescence of fine particles can ensure excellent on-press developability, it has a problem of being inferior in press life because the adhesion between an aluminum substrate and the images formed is weak, and besides, the image strength is low.
As a solution to the problem, it is known to utilize a phosphoric acid bath anodic oxidation layer having high adhesive strength. However, this method has a drawback of causing deterioration in ink eliminability.
Further, JP-A-8-48020 discloses the method in which an ink-receptive heat-sensitive layer is provided on a porous water-receptive substrate and exposed to infrared ray laser beams, thereby thermally adhering the heat-sensitive layer to the substrate. However, the ink-receptive coating is inferior in on-press developability, and scum on the ink-receptive heat-sensitive layer causes a trouble of adhering to ink rollers or printed matters.
An object of the present invention is to provide a heat-sensitive lithographic printing plate precursor capable of overcoming the defects of prior arts. That is, the present invention aims to provide a heat-sensitive lithographic printing plate precursor which has excellent on-press developability, and can ensure a long press life, high scumming resistance and high ink eliminability in the printing process.
As a result of our intensive studies, it has been found that the aforedescribed object can be achieved by controlling the average pore diameter (i.e., the average pore size) of micropores present in an anodically treated substrate to a specified range, or by using a substrate immersed in a water solution of hydrophilic compound or coated with a water-receptive subbing layer after a pore-widening treatment. Specifically, the following are embodiments of the present invention:
1. A heat-sensitive lithographic printing plate precursor which comprises a substrate having thereon an anodic oxidation layer, the printing plate precursor comprising a hydrophilic layer containing at least one kind of fine particles selected from the group consisting of heat-fusible hydrophobic thermoplastic fine particles, finely divided polymers having heat-reactive functional groups and microcapsules in which compounds having heat-reactive functional groups are encapsulated, and with the anodic oxidation layer having a surface over which micropores having an average pore size of 6 to 40 nm are uniformly distributed.
2. The heat-sensitive lithographic printing plate precursor according to Embodiment 1, wherein the average pore size of micropores is controlled to 6 to 40 nm by subjecting the substrate having an anodic oxidation layer to a pore-widening treatment by immersion in sulfuric acid, phosphoric acid, a mixture of these acids or an aqueous alkali solution adjusted to pH 11-13, or to the pore-widening treatment and then to a pore-sealing treatment.
3. The heat-sensitive lithographic printing plate precursor according to Embodiment 1, wherein the average pore size of micropores is controlled to 6 to 40 nm by subjecting the substrate having an anodic oxidation layer to a pore-widening treatment by immersion in an aqueous sulfuric acid solution and then to a pore-sealing treatment.
4. The heat-sensitive lithographic printing plate precursor according to Embodiment 2 or 3, wherein the pore-sealing treatment is a treatment by steam.
5. A heat-sensitive lithographic printing plate precursor which comprises a substrate having thereon an anodic oxidation layer, the printing plate precursor comprising a hydrophilic layer containing at least one kind of fine particles selected from the group consisting of heat-fusible hydrophobic thermoplastic fine particles, finely divided polymers having heat-reactive functional groups and microcapsules in which compounds having heat-reactive functional groups are encapsulated, and the anodic oxidation layer having a surface over which micropores are subjected to a pore-widening treatment and then to an immersion treatment in an aqueous solution containing a hydrophilic compound.
6. A heat-sensitive lithographic printing plate precursor which comprises a substrate having thereon an anodic oxidation layer, with the printing plate precursor comprising a hydrophilic layer containing at least one kind of fine particles selected from the group consisting of heat-fusible hydrophobic thermoplastic fine particles, finely divided polymers having heat-reactive functional groups and microcapsules in which compounds having heat-reactive functional groups are encapsulated, and the anodic oxidation layer having a surface over which micropores subjected to a pore-widening treatment are uniformly distributed and further having on the surface a subbing layer comprising a water-soluble resin containing carboxyl or carboxylato groups and a water-soluble salt containing at least one metal selected from the group consisting of zinc, calcium, magnesium, barium, strontium, cobalt, manganese and nickel.
7. The heat-sensitive lithographic printing plate precursor according to Embodiment 5 or 6, wherein the pore-widening treatment is a treatment carried out by immersing the substrate having an anodic oxidation layer in an aqueous solution of sulfuric acid or an aqueous alkali solution adjusted to pH 11-13.
8. The heat-sensitive lithographic printing plate precursor according to Embodiment 5, wherein the hydrophilic compound is at least one compound selected from the group consisting of alkali metal silicates, zirconium potassium fluoride, mixtures of alkali metal phosphates and alkali metal fluorides, polyvinylphosphonic acid, sodium lignin sulfonate and saponin.
9. The heat-sensitive lithographic printing plate precursor according to Embodiment 6, wherein the water-soluble resin containing carboxyl or carboxylato groups is at least one resin selected from the group consisting of carboxymethyl cellulose, polyacrylic acid and acrylamide-methacrylic acid copolymer.
10. The heat-sensitive lithographic printing plate precursor according to Embodiment 6, wherein the water-soluble salt of metal is an acetate of at least one metal selected from the group consisting of magnesium, nickel, manganese, calcium and nickel.
11. The heat-sensitive lithographic printing plate precursor according to any of Embodiments 1 to 10, wherein the hydrophilic layer has thereon a water-soluble overcoat layer.
12. The heat-sensitive lithographic printing plate precursor according to Embodiment 11, wherein the water-soluble overcoat layer contains a light-to-heat converting agent.
13. A method of making a printing plate from a heat-sensitive lithographic printing plate precursor and printing from the printing plate made, comprising steps of image exposing a heat-sensitive lithographic printing plate precursor as described in any of Embodiments 1 to 12, using laser beams, mounting the printing plate precursor image wise exposed in a printing machine as it is without any further processing and then performing printing operations; or comprising steps of mounting in a printing machine a heat-sensitive lithographic printing plate precursor as described in any of Embodiments 1 to 12, imagewise exposing the printing plate precursor mounted in the printing machine, using laser beams and then performing printing operations without any further processing.